I use Emacs both on Linux Mint and macOS. I use iSpell on both. On Linux, when I check the region, I have around 20 options for a misspelled word; on macOS, the same word will only display 2 or 3 options.
I installed Emacs with brew and ispell as well. ispell-program-name is pointing at /opt/homebrew/bin/ispell which seems OK to me.
How do I get ispell to show the same number of words?
ispellon Linux? It's often an "aliased" to the superioraspellorhunspell.ispell-program-name, preferringaspelloverispell. You can see what's happening inlisp/textmodes/ispell.elor here